Structure of the brain has been examined in four species of insects : adults and larvae of blowflies Phormia regina Meigen, adult cockroaches Periplaneta americana, worker honeybees Apis mellifera, and adults and larvae of tiger beetles Cicindela chinensis.The optic lobe of the compound eye consists of three neuropils : lamina, medulla and lobula neuropils : The lamina and medulla neuropils are organized retinotopically, whereas lobula neuropil is organized to integrate such retinotopic visual information for abstract specific visual information. The optic lobe of the tiger beetle larva consists of two neuropil regions : retinotopic lamina region and integrative medulla region. The basic design of optic neuropil appears to be genetically determined, because the neuropil structure is normally differentiated in the larval and pupal lifves under constant dark. But, some minute changes occurred in the fly optic neuropil structure reared under light-deprived condition : axons of retinal int
… Moreerneurons decreased. Such changes were statistically significant, and may be related to plastic nature of the neuropil structure.Terminations of sensory interneurons of various modalities including afferent axons of the optic neuropil and output axons of olfactory lobe have been examined in the brain of the four species. Those sensory interneurons terminate in the mushroom body in the protocerebrum suggesting multimodal sensory integration there. The mushroom body also appears to play an primary role for initiation of voluntary behavior, because some neurons fire prior initiation of locomotion.Plastic changes of behavior were observed in locomotion of cockroaches triggered by air puffs, predatory and escape responses of tiger beetle larva and visual behavior of the worker honeybees. Such changes must be rooted in plastic changes of neural networks, which comprise morphological and physiological basis of higher neural function such as memory and learning. In this research program neural activities concerning to such higher function were recorded in cockroach brain. In the cockroach that was trained to learn some visual cue to avoid an uncomfortable place, the neurons exclusively responding to such visual cues were found.These results may be physiological counterpart of learning and are suggestive plastic nature of the insect brain for higher neural function. Less